The reduction of thin films to nanometer dimensions for new technologies requires excellent control of film thickness, morphology, crystallinity, and conformality. Many of these requirements can be achieved by growth controlled at single atomic layers by means of binary reaction sequence chemistry. Furthermore, low deposition temperatures are often required, for example due to restricted thermal budget and interlayer diffusion that may destroy the properties of nanoscale devices. Atomic layer deposition (ALD) may be preferred or required for some advanced manufacturing processes due to its superior conformal deposition and film thickness control, and current ALD processes are often performed at lower temperatures than chemical vapor deposition (CVD) processes. However, these ALD processes are often at temperatures too high to prevent unwanted oxidation of a substrate.
Silicon nitride (SiN) films are widely used in semiconductor devices and ultra-large-scale integrated (ULSI) circuits. For example, silicon nitride films have been widely used in semiconductor devices as diffusion barriers for dopants and metals, as etch-stop films during etching of fine features, as final passivation films for encapsulation of fabricated devices, and in many other ways.
Silicon dioxide (SiO2) is the preferred dielectric material for many current and future microelectronic devices. Conformal SiO2 films may be used as interface layers in high aspect ratio trench capacitors to extend dynamic random access memory (DRAM) to the 1-gigabyte regime. Uniform SiO2 films appear on extremely large substrates for flat panel displays. Furthermore, very thin SiO2 films can be used in multilayer and nanolaminate structures to tailor mechanical, electrical, and optical thin film properties. Low-temperature SiO2 deposition techniques will facilitate the use of a SiO2 film as a protective coating or insulator on polymeric or biological materials.
In ALD, self-terminating surface reactions applied in a binary reaction sequence can be used to achieve atomic layer control of thin film growth. Prior work on SiO2 atomic layer-controlled growth has focused on dividing the SiCl4+2H2O→SiO2+4HCl reaction into two half -reactions:Si—OH*+SiCl4→SiO—Si(—Cl*)3+HCl  (A)Si—Cl*+H2O→Si—OH*+HCl  (B)
where the asterisks (*) designate the surface species. The SiCl4 and H2O half-reactions are performed in an ABAB . . . binary sequence to grow a SiO2 film with a desired thickness.
In each half-reaction, a gas-phase precursor reacts with a surface functional group. The surface reaction continues until the initial surface functional groups (Si—OH) have reacted and have been replaced with the new functional groups (Si—Cl*). The half-reactions are self-limiting; once a half-reaction goes to completion, additional reactant produces no additional film growth. Successive application of the A and B half-reactions has produced atomic layer-controlled SiO2 deposition. Atomic force microscope (AFM) images have revealed that the SiO2 films deposited on Si(100) by ALD can be highly conformal and extremely smooth.
Drawbacks of SiO2 atomic layer-controlled growth include the high substrate temperatures (>300° C.) and large reactant exposures (>109 Langmuirs (1 L=10−6 Torr-sec)) required for the surface half-reactions to reach completion. Recent discoveries have demonstrated that the high reaction temperatures and large precursor fluxes can be avoided by catalyzing the surface reactions. In one example, organic base pyridine (C5H5N) may be utilized as a catalyst as pyridine interacts strongly with the surface functional groups and reactants present during both the A and B half-reactions of the binary reaction sequence. As a result, SiO2 films have been deposited by means of such catalyzed binary reaction sequence chemistry at temperatures below about 100° C. or even as low as room temperature using greatly reduced reactant flux required for complete reactions.
However, catalyst-based ALD of SiO2 film in the prior art suffers from several drawbacks. For example, chlorine (Cl) and carbon (C) impurities are frequently incorporated into the SiO2 film during deposition, where the carbon impurities likely originate from undesirable decomposition of the catalyst. Post-deposition processing such as high temperature oxidation may be required to remove these impurities and any film defects associated with impurity incorporation, and to further improve the material and electrical properties of the deposited SiO2 film. However, high temperature post-deposition processing may not be possible or desired since it can exceed the thermal budget needed for temperature sensitive materials and manufacturing processes. Furthermore, high temperature post-deposition processing can reduce or eliminate the benefits gained by the low temperature catalyst-assisted ALD processing, in particular if long processing times are required for the post-deposition processing. For example, high-temperature post-deposition processing has been observed to increase gate oxide thickness.
As a result, there is a need for improving catalyst-based ALD of silicon-containing films, such as SiO2 and SiN films, that reduces or eliminates undesired high-temperature post-deposition processing performed to remove film impurities and film defects associated with impurity incorporation.